Method for independently detecting signals in a double-junction filterless CMOS color imager cell

Abstract

A double-junction complimentary metal-oxide-semiconductor (CMOS) filterless color imager cell is provided. The imager cell is fabricated from a silicon-on-insulator (SOI) substrate including a silicon (Si) substrate, a silicon dioxide insulator overlying the substrate, and a Si top layer overlying the insulator. A photodiode set is formed in the SOI substrate, including a first and second photodiode formed as a double-junction structure in the Si substrate. A third photodiode is formed in the Si top layer. A (imager sensing) transistor set is formed in the top Si layer. The transistor set is connected to the photodiode set and detects an independent output signal for each photodiode. The transistor set may be an eight-transistor (8T), a nine-transistor (9T), or an eleven-transistor (11T) cell.

1. A method for independently detecting signals from a double-junction complimentary metal-oxide-semiconductor (CMOS) color imager cell, the method comprising:
 providing a silicon (Si) substrate with a double-junction structure of first and second photodiodes sharing a common node; 
 selectively connecting the common node to a reference voltage; 
 reading a first photodiode voltage; 
 selectively disconnecting the common node from the reference voltage; 
 reading a second photodiode voltage; 
 wherein providing the double-junction structure includes providing first and second photodiodes sharing a common cathode, with an anode of the second photodiode connected to the reference voltage; and, 
 wherein selectively connecting the common node to a reference voltage includes connecting the cathodes of the first and second photodiodes to the reference voltage. 
 
   
   
     2. The method of  claim 1  wherein reading the first photodiode voltage includes:
 subsequent to connecting the first and second photodiode cathodes to the reference voltage, applying a voltage to the first photodiode anode; and, 
 reading the voltage on the first photodiode anode; and, 
 wherein reading the second photodiode voltage includes: 
 subsequent to disconnecting the second photodiode cathode from the reference voltage, applying a voltage to the second photodiode cathode; and, 
 reading the voltage on the second photodiode cathode. 
 
   
   
     3. The method of  claim 1  wherein providing the double-junction structure includes providing the first photodiode pn junction between a p-doped (p+) region and an n-doped well (n-well) underlying the p-doled region, and providing the second photodiode pn junction between a p-doped substrate and the n-well overlying the p-doped substrate. 
   
   
     4. The method of  claim 1  wherein providing the double-junction structure additionally includes providing a Si-on-insulator (SOI) substrate with the first and second photodiodes formed in the SOI substrate, and a third photodiode formed in a SOI top Si layer; and,
 the method further comprising: 
 reading a third photodiode voltage. 
 
   
   
     5. The method of  claim 4  further comprising:
 resetting the first and third photodiode voltages; and, 
 where reading the first and third photodiode voltages includes:
 subsequent to resetting the first and third photodiode voltages, simultaneously reading the first and third photodiode voltages; and, 
 reading the first photodiode voltage independent of detecting the third photodiode voltage. 
 
 
   
   
     6. The method of  claim 5  further comprising:
 subsequent to reading the first and third photodiode voltages, resetting the second photodiode voltage; and, 
 wherein reading the second photodiode voltage includes reading the second photodiode voltage independent of reading the first and third photodiode voltages. 
 
   
   
     7. The method of  claim 4  wherein reading the third photodiode voltage includes reading a signal associated with the detection of a blue light spectrum;
 wherein reading the first photodiode voltage includes reading a signal associated with the detection of a green light spectrum; and, 
 wherein reading the second photodiode voltage includes reading a signal associated with the detection of a red light spectrum.